Gyroscopic Boat Roll Stabilizer

ABSTRACT

A gyroscopic roll stabilizer comprises a gimbal having a support frame and enclosure configured to maintain a below-ambient pressure, a flywheel assembly including a flywheel and flywheel shaft, one or more bearings for rotatably mounting the flywheel inside the enclosure, a motor for rotating the flywheel, and bearing cooling system for cooling the bearings supporting the flywheel. The bearing cooling system enables heat generated by the bearings to be transferred through the flywheel shaft to a heat sink disposed within a cavity in the end of the flywheel shaft, or to a liquid coolant circulating within the cavity.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/678,422, filed May 31, 2018, and U.S. Provisional PatentApplication Ser. No. 62/768,356, filed Nov. 16, 2018, the disclosures ofwhich are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to boat roll stabilizers forreducing the sideways rolling motion of a boat and, more particularly,to controlled moment gyroscopes for reducing the roll of a boat based onthe gyroscopic effect.

BACKGROUND

The sideways rolling motion of a boat can create safety problems forpassengers and crew on boats, as well as cause discomfort to passengersnot accustomed to the rolling motion of the boat. A number oftechnologies currently exist to reduce the sideways rolling motion of aboat. One technology currently in use is active fin stabilization.Stabilizer fins are attached to the hull of the boat beneath thewaterline and generate lift to reduce the roll of the boat due to windor waves. In the case of active fin stabilization, the motion of theboat is sensed and the angle of the fin is controlled based on themotion of the boat to generate a force to counteract the roll. Finstabilization is most commonly used on large boats and are effectivewhen the boat is underway. Fin stabilization technology is not usedfrequently in smaller boats and is generally not effective when the boatis at rest. Stabilizer fins also add to the drag of the hull and aresusceptible to damage.

Gyroscopic boat stabilization is another technology for roll suppressionthat is based on the gyroscopic effect. A control moment gyroscope (CMG)is mounted in the boat and generates a torque that can be used tocounteract the rolling motion of the boat. The CMG includes a flywheelthat spins at a high speed. A controller senses the attitude of the boatand uses the energy stored in the flywheel to “correct” the attitude ofthe boat by applying a torque to the hull counteracting the rollingmotion of the boat. CMGs work not only when a boat is underway, but alsowhen the boat is at rest. CMGs are also less expensive than stabilizerfins, do not add to the drag of the hull, and are not exposed to risk ofdamage.

Although, CMGs are gaining in popularity, particularly for smallerfishing boats and yachts, this technology has some limitations. Theenergy used to counteract the rolling motion of the boat comes from therotation of the flywheel at a high rate of speed. Consequently, heatbuilds up in the bearings supporting the flywheel and bearing failurecan result, which presents an extreme hazard for the boat due to theamount of energy stored in the flywheel. In order to obtain the highspin rate, the flywheel is typically contained in a vacuum enclosure,which makes heat dissipation problematic.

Another problem with existing CMGs is that it takes a significant amountof time for the flywheel to “spin up,” i.e., to obtain its desiredoperating speed. In some CMGs currently on the market, it can take aslong as 70 minutes before the CMG is ready for use. The long “spin up”period means that the CMG cannot be used for trips of short duration,which comprises a majority of boating occasions. It also takes a longtime for the flywheel to “spin down,” typically in the order of severalhours. While the flywheel is spinning down, it continues to make awhining noise, which can be disruptive to the enjoyment of the occupantsafter the boat has arrived at its destination on the water or returnedto the docks following a day of boating.

SUMMARY

The present disclosure relates to a gyroscopic roll stabilizer for aboat. The gyroscopic roll stabilizer includes an enclosure mounted to agimbal and configured to maintain a below-ambient pressure, a flywheelassembly including a flywheel and flywheel shaft, one or more bearingsfor rotatably mounting the flywheel assembly inside the enclosure, amotor for rotating the flywheel, and a bearing cooling system forcooling the bearings supporting the flywheel. In one embodiment, thebearing cooling system comprises a heat sink that is disposed within acavity formed within the end of the flywheel shaft. Heat is transferredfrom the flywheel shaft to the heat sink and then by solid and/or liquidconduction to the heat exchanger. In another embodiment, cooling isachieved by delivering a liquid coolant into a tapered cavity in the endof the flywheel shaft. The cavity is shaped so that the centrifugalforce causes the liquid coolant to flow towards the open end of theshaft, where the liquid coolant is collected by a fluid collectionsystem.

One aspect of the disclosure comprises methods of operating a CMGconfigured to function as a roll stabilizer for a boat. The CMG includesa flywheel assembly in an enclosure mounted in a gimbal for rotationabout a gimbal axis and maintained at below ambient pressure to providea counter torque for roll stabilization. The flywheel assembly includesa flywheel and a flywheel shaft. In one embodiment, the method comprisesrotating the flywheel assembly, transferring heat generated by bearingssupporting the flywheel assembly through the flywheel shaft to a heattransfer member extending into a cavity in one end of the flywheelshaft, and transferring the heat by solid conduction through the heattransfer member to an exterior of the enclosure.

In another embodiment, the method comprises rotating the flywheelassembly, circulating a liquid coolant through a cavity formed in oneend of the flywheel shaft, and transferring heat generated by bearingssupporting the flywheel assembly through the flywheel shaft to theliquid coolant.

Another aspect of the disclosure comprises a gyroscopic roll stabilizerfor a boat. In one embodiment, the gyroscopic boat roll stabilizercomprises an enclosure mounted to a gimbal for rotation about a gimbalaxis and configured to maintain a below-ambient pressure, a flywheelassembly including a flywheel and flywheel shaft, one or more bearingsfor rotatably mounting the flywheel assembly inside the enclosure, amotor for rotating the flywheel assembly, an open-ended cavity formed inan end of the flywheel shaft, and a heat transfer member extending intothe cavity for transferring heat from the flywheel shaft to an exteriorof the enclosure

In another embodiment, the gyroscopic boat roll stabilizer comprises anenclosure mounted to a gimbal for rotation about a gimbal axis andconfigured to maintain a below-ambient pressure, a flywheel assemblyincluding a flywheel and flywheel shaft, one or more bearings forrotatably mounting the flywheel assembly inside the enclosure, a motorfor rotating the flywheel assembly, an open-ended cavity formed in anend of the flywheel shaft, a coolant delivery system for delivering aliquid coolant to the cavity, and a collection system disposed adjacentthe end of the flywheel shaft for collecting the liquid coolantdelivered to the cavity of the flywheel shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a boat equipped with a CMG as hereindescribed.

FIG. 2 is an elevation view of a CMG configured as a boat rollstabilizer according to a first embodiment.

FIG. 3 is a section view through the enclosure of the CMG according to afirst embodiment

FIG. 4 is a partial section view illustrating the bearing cooling systemaccording to the first embodiment.

FIG. 5 illustrates a cooling circuit for a CMG.

FIG. 6 illustrates a torque control system for the CMG.

FIG. 7 is a partial section view illustrating the bearing cooling systemaccording to a second embodiment.

FIG. 8 is a partial section view illustrating the bearing cooling systemaccording to a third embodiment.

FIG. 9 is a partial section view illustrating the bearing cooling systemaccording to a fourth embodiment.

FIG. 10 is a partial section view illustrating the bearing coolingsystem according to a fifth embodiment.

FIG. 11 is a partial section view illustrating the bearing coolingsystem according to a sixth embodiment.

FIG. 12 is a partial section view illustrating the bearing coolingsystem according to a seventh embodiment.

DETAILED DESCRIPTION

Referring now to the drawings, FIGS. 1A and 1B illustrate a CMG 10mounted in a boat 5 for roll stabilization. Multiple embodiments of theCMG 10 are described. For convenience, similar reference numbers areused in the following description of the embodiments to indicate similarelements in each of the embodiments.

Referring now to FIGS. 2 and 3, the main functional elements of the CMG10 comprise a single-axis gimbal 20, an enclosure 30 mounted to thegimbal 20 for rotation about a gimbal axis G, a flywheel assembly 40mounted by bearings 50 inside the enclosure, a motor 60 to rotate theflywheel assembly 40, and a torque control system 70 (FIG. 5) to controlprecession of the flywheel assembly 40 so that the energy of theflywheel assembly 40 is transferred to the hull of the boat 5 tocounteract rolling motions. Each of the embodiments further comprises abearing cooling system 100 to cool the flywheel bearings 46. Variousdesigns of the bearing cooling system 100 are shown in FIGS. 4 and 7-12.

The gimbal 20 comprises a support frame 22 that is configured to besecurely mounted in the boat 5. Preferably, the gimbal 20 is mountedalong a longitudinal axis L of the boat 5 with the gimbal axis Gextending transverse to the longitudinal axis L. Conventionally, thegimbal 20 is mounted in the hull of the boat 5, but could be mounted atany location. The support frame 22 of the gimbal 20 comprises a base 24and two spaced-apart supports 26. A bearing 28 is mounted on eachsupport 26 for rotatably mounting the enclosure 30 to the supports 26.For this purpose, the enclosure 30 includes two gimbal shafts 32projecting from diametrically opposed sides of the enclosure 30. Thegimbal shafts 32 are rotatably journaled in the gimbal bearings 28 toallow the enclosure 30 and flywheel assembly 40 to rotate or precessabout the gimbal axis G in the fore and aft directions.

The basic elements of enclosure 30 are the same in the variousembodiments described herein but vary in some details depending on thedesign of the bearing cooling system 100. The enclosure 30 is generallyspherical in form and comprises two main housing sections 34 and twocover plates 36. The two main housing sections 34 join along a planethat bisects the spherical enclosure 30. The cover plates 36 join themain housing sections 34 along respective planes closer to the “poles”of the spherical enclosure 30. All joints in the enclosure 30 are sealedto maintain a below-ambient pressure within the enclosure 30 to reduceaerodynamic drag on the flywheel assembly 40. Although the constructionof the enclosure 30 is generally the same in the embodiments hereindescribed, the details of the housing sections 34 and cover plates 35vary as described more fully below depending on the design of thebearing cooling system used.

Referring to FIG. 3, the flywheel assembly 40 comprises a flywheel 42and flywheel shaft 44 that is mounted for rotation inside the enclosure30 of the gimbal 20 so that the axis of rotation F of the flywheelassembly 40 is perpendicular to the gimbal axis G. Thus, when the boat 5is level, the axis of the flywheel shaft 44 will be in the verticaldirection, i.e. perpendicular to the deck of the boat. The flywheel 42and shaft 44 may be formed as a unitary piece, or may comprise twoseparate components. In one exemplary embodiment, the diameter and theflywheel 42 is approximately 20.5 inches and the flywheel assembly 40has a total weight of about 614 lbs. The flywheel assembly 40 has amoment of inertia of about 32,273 lb int. When rotated at a rate of 9000rpm, the angular momentum of the flywheel assembly 40 is about 211,225lbm ft²/s.

The flywheel assembly 40 is supported by upper and lower bearingassemblies inside the enclosure 30. Each bearing assembly comprises abearing 50 mounted within a bearing block 58. Each bearing 50 comprisesan inner race 52 that contacts and rotates with the flywheel shaft 44,an outer race 54 that is mounted inside the bearing block 58, and a ball56 disposed between the inner and outer races 52, 54. The bearing blocks58 are secured to the interior of the enclosure. Seals (not shown) aredisposed on the top and bottom of the bearings 50 to contain lubricantin the bearings 50.

The motor 60 rotates the flywheel assembly 40 at a high rate of speed(e.g., 9000 rpm). The motor 60 includes a rotor 62 that connects to theflywheel shaft 44 and a stator 64 that this secured to the enclosure 30by any suitable mounting system. Although the motor 60 is shown mountedinside the enclosure 30, it is also possible to mount the motor 60 onthe exterior of the enclosure 30. In one embodiment, the motor 60operates on 230 Volt single phase AC power and is able to accelerate aflywheel assembly with a moment of inertia of about 32,273 lb in²flywheel from rest to a rotational speed of 9000 rpm preferably in about30 minutes or less for an average acceleration of about 5 rpm/s, andmore preferably in about 20 minutes or less for an average accelerationof about 7.75 rpm/s, and even more preferably in about 10 minutes orless for an average acceleration of about 15 rpm/s (or 1.57 radians/s²).

The torque control system 70, shown in FIG. 5, controls the rate ofprecession of the flywheel assembly 40 about the gimbal axis G. Therolling motion of a boat 5 caused by wave action can be characterized bya roll angle and roll rate. The rolling motion causes the flywheel 42 toprecess about the gimbal axis G. Sensors 74, 76 measure the roll angleand roll rate respectively, which are fed to a controller 72. Thecontroller 102 generates control signals to control an active brakingsystem or other torque applying device 78 that controls the rate ofprecession of the flywheel assembly 40. By controlling the rate ofprecession, the flywheel assembly 40 generates a torque in opposition tothe rolling motion. This torque is transferred through the gimbal 20 tothe boat 5 to dampen the roll of the boat 5. An example of the activebraking system 78 is described in U.S. Provisional Application62/828,845 filed Apr. 3, 2019 titled, “Braking System For GyroscopicBoat Roll Stabilizer”, which is incorporated herein its entirety byreference.

When the flywheel assembly 40 rotates at high speed, the bearings 50 andmotor 60 will generate a substantial amount of heat, which could lead todangerous bearing failure. Conventional air and liquid coolingtechniques are not suitable for bearings 50 or other heat generatingcomponents contained within a vacuum environment. Various embodiments ofthe bearing cooling system 100 are disclosed herein allow cooling ofbearings 50 and other heat generating components contained within theenclosure without direct contact of the oil or liquid coolant with thebearings 50 or other heat generating components, which would result inhigh frictional losses. In general, heat is transferred by solid and/orliquid conduction to a heat sink that is cooled by oil, glycol or otherliquid coolant. Oil or liquid cooling enables more heat to be dissipatedcompared to air cooling or gaseous convection and conduction. Relianceon gaseous convection and conduction in existing CMGs imposes severelimitations on the amount of heat that can be dissipated because theinterior of the enclosure 30 is typically maintained at a below ambientpressure. The limited heat transfer capacity in prior art CMGs 10imposes severe limitations on the size of the electric motor that isused, which in turn limits the time to engage and use the CMG 10.Because the electric motor in conventional CMGs is undersized to avoidheat generation, conventional CMGs require significant time toaccelerate the flywheel assembly 40 to a speed that provides the desiredcounter-torque and roll stabilization. Providing more efficient coolingof the bearings 50 as herein described enables use of a larger and morepowerful motor 60 and faster acceleration of the flywheel assembly 40 sothat the benefits of using the CMG 10 can be obtained in significantlyshorter time periods.

FIG. 6 is a schematic diagram of a cooling circuit 80 for circulatingthe liquid coolant. A fluid reservoir 82 contains the liquid coolantwhich is circulated in a “closed” circuit by a fluid pump 84. The fluidreservoir 82 may include a heat exchanger 83 to cool the liquid coolantin the fluid reservoir 82. After collecting heat dissipated by thebearings 50, the liquid coolant passes through the heat exchanger 86where it adsorbs and carries away heat generated by the bearings 50 asdescribed more fully below. In some embodiments, heat is transferredfrom the flywheel shaft 44 to a heat sink and then by solid and liquidconduction to the heat exchanger 86. In other embodiments, heat istransferred from the flywheel shaft 44 to the liquid coolant which iscirculated through a cavity 46 in the flywheel shaft 44. In thisembodiment, the heat transfer to the liquid coolant occurs within thecavity 46 of the flywheel shaft 44 so the heat exchanger 86 is notrequired. In some embodiments, a scavenging circuit 88 is provided tocollect liquid coolant that seeps into the interior of the enclosure 30and return the liquid coolant to the fluid reservoir 82.

FIG. 4 illustrates one embodiment of a bearing cooling system 100 usinga heat sink to dissipate heat generated by the bearings 50 and/or motor60. The upper portion of the flywheel shaft 44 is secured within abearings 50 that is, in turn, secured within the enclosure 30. Eachbearing 50 includes an outer race 54, balls 56 and an inner race 52 thatengages the flywheel shaft 44 and rotates therewith. The flywheel shaft44 includes a cavity 46 at each end thereof. The cavity 46 in each endof the flywheel shaft 44 is open at one end and includes a side wall anda bottom wall.

A heat transfer member 102 that functions as a heat sink is suspended inthe cavity 46 as hereinafter described. The heat transfer member 102does not directly engage the side or bottom walls of the cavity 46.Rather, the outer surface of the heat transfer member 102 is spaced fromthe side and bottom walls of the cavity 46. In one embodiment, thespacing between the heat transfer member 102 and the walls of the cavity46 is approximately 0.062″. Various materials can be used for the heattransfer member 102 discussed herein. Preferably, copper, aluminum, oralloys thereof are used because of their relatively high thermalconductivity.

A heat transfer medium is contained in the gap between the heat transfermember 102 and the walls of the cavity 46. As one example, the heattransfer medium comprises a low vapor fluid that is suitable for the lowpressure environment in the enclosure 30. A low vapor fluid is a liquid,such as oil, that has a relatively low boiling point compared to waterand is suitable for employment in a vacuum environment. For example,aerospace lubricants, such as perfluoropolyether (PFPE) lubricants,designed for vacuum environments can be used as the heat exchangemedium. The low vapor fluid enables transfer of heat from the flywheelshaft 44 to the heat transfer member 102 by liquid conduction and liquidconvection. A labyrinth seal 110 extends around the heat transfer member102 and effectively seals the cavity 46 such that the heat transfermedium is maintained within the cavity 46. The labyrinth seal 110 ispreferably fixed to the heat transfer member 102, which means that theflywheel shaft 44 rotates around the labyrinth seal 110.

As seen in FIG. 4, heat transfer member 102 projects from cavity 46,through an opening in a cover plate 36 forming a part of the enclosure30, and into a heat exchanger 86. Seals 108 located in correspondinggrooves in the cover plate 36 maintain vacuum within the enclosure 30.The heat exchanger 86 is mounted to the exterior surface of the coverplate 36. The heat exchanger 86 comprises a housing 106 and a heatexchange plate 104 confined within the housing 106. The heat transfermember 102 is secured by a fastener 103 to the heat exchange plate 104so that the heat transfer member 102 is effectively suspended in thecavity 46 formed in the flywheel shaft 44. More particularly, the heatexchange plate 104 includes a recess in the bottom surface thereof thatreceives the end of the of the heat transfer member 102. The surfacecontact between the end of the heat transfer member 102 and the heatexchange plate 104 facilitates the efficient transfer of heat by solidconduction from the heat transfer member 102 to the heat exchange plate104.

A liquid coolant, such as a glycol coolant, is circulated through theheat exchanger 86 to absorb and carry heat away from the heat exchangeplate 104 as shown in FIG. 5. The upper surface of the heat exchangeplate 104 can be provided with fluid channels and/or cooling fins toincrease surface area of the heat exchange plate 104 and to facilitateheat transfer from the heat exchange plate 104 to the liquid coolant.

Heat is generated in the inner and outer races of the bearing assemblies50 due to the high side loads generated from the CMG's torque as theenclosure 30 rotates about the gimbal axis G. The outer race 54 has acontinuous heat conductive path through the enclosure 30 which permitsthe heat associated with the outer race 54 to be rejected into theatmosphere. The inner race 52 requires a heat sink path through parts ofthe enclosure 30. In this embodiment, heat from the inner race 52 of thebearing assembly 50 is transferred by solid conduction to the flywheelshaft 44. The heat is then transferred by liquid conduction from theflywheel shaft 44 to the heat transfer member 102, and by solidconduction through the heat transfer member 102 to the heat exchangeplate 104 that continuously rejects the heat into surrounding liquidcoolant. In some embodiments, the heat exchange 86 could employ air orgas cooling rather than liquid cooling.

FIG. 7 illustrates an alternate bearing cooling system 100 that alsouses a heat sink. This bearing cooling system 100 in FIG. 7 is similarto the design shown in FIG. 4. The main differences lie in the shapes ofthe heat transfer member 102, labyrinth seal 110, and the heat exchangeplate 104. In this embodiment, the heat transfer member 102 includes achannel that increases the surface area exposed to the heat transfermedium. The heat exchange plate 104, in contrast to the previousembodiment, has a smooth top surface without grooves or vanes. The heattransfer path, however, is essentially the same. That is, heatassociated with the inner race 52 is transferred to the flywheel shaft44 by solid conduction. The cavity 46 formed in the flywheel shaft 44,like the above design, is configured to hold a low vapor fluid so thatheat is transferred by liquid conduction from the flywheel shaft 44through the low vapor fluid to the lower portion of a heat transfermember 102. Thereafter, heat in the heat transfer member 102 istransferred by solid conduction to the heat exchange plate 104. A liquidcoolant is circulated into, through and out the heat exchanger 86. Indoing so, the liquid coolant contacts the heat exchange plate 104 andheat associated with the heat exchange plate 104 is transferred to thecirculating liquid coolant.

FIG. 8 is another alternative design for a bearing cooling system 100for a gyroscopic boat stabilize using a heat sink. This design issimilar in concept to the preceding designs but differs in a number ofrespects. First, there are two heat transfer members 102A and 102B. Heattransfer member 102A is inserted into the cavity 46 in the flywheelshaft 44 and rotates with the flywheel shaft 44. Close surface contractbetween the walls of the cavity 46 and the heat transfer member 102Afacilitates heat transfer by solid conduction from the flywheel shaft 44to the heat transfer member 102A. Heat transfer member 102B passesthrough an opening in the cover plate 36 and is axially aligned with thefirst heat transfer member 102A. One end of the heat transfer member102B connects to a heat exchange plate 104. A small gap is maintainedbetween the abutting ends of the heat transfer members 102A and 102B ashereinafter described. A light film of conductive low vapor grease isapplied to the interface between the abutting ends of the heat transfermembers 102A and 102B to prevent wear and facilitate heat transfer fromheat transfer member 102A and heat transfer member 102B. The grease isprevented from escaping by a labyrinth seal 114. In the course ofdissipating heat from the inner race 52 of a bearing assembly 50, heatis transferred from the inner heat transfer member 102A through the thinfilm of grease to the outer heat transfer member 102B.

A pre-loaded spring 112 is interposed between the heat exchange plate104 and the cover plate 36 of the enclosure 30. The reason for this isthat the vacuum in the enclosure 30 tends to pull the outer heattransfer member 102B inwardly. Thus, the spring 112 is employed tocounterbalance the vacuum force and to maintain a desired spacingbetween the heat transfer members 102A and 102B.

The heat transfer path in this design is essentially the same as the twoprevious embodiments. Heat associated with the inner race 52 of thebearing assembly 50 is transferred by solid conduction from the innerrace 52 to the flywheel shaft 44 and from the flywheel shaft 44 to firstheat transfer member 102A. Heat in the first heat transfer member 102Ais transferred by conduction through the thin film of grease to thesecond heat transfer member 102B, and by solid conduction from the heattransfer member 102B to the heat exchange plate 104. The liquid coolantcirculating in the heat exchanger 86 adsorbs and carries away the heatin the heat exchange plate 104.

FIGS. 9-14 illustrate embodiments of a bearing cooling system 100 inwhich heat is transferred to a liquid coolant that is circulated in thecavity 46 in the end of the flywheel shaft 44. In this case, the heattransfer to the liquid coolant occurs within the cavity 46 in theflywheel shaft 44. The following discussion will focus primarily on theelements involved in the heat transfer. Except where noted below, thebasic design of the gimbal 20, enclosure, 30, flywheel 40, bearingassemblies 50 and motor 60 (not shown) are essentially the same aspreviously described. Therefore, the following description will notreiterate all of the details of these elements. In the embodiments shownin FIGS. 9 and 10, the ends of the flywheel shaft 44 include speciallyformed cavities 46 into which the liquid coolant is delivered orinjected. Each cavity 46 extends along the longitudinal axis of theflywheel shaft 44 so that the bottom or closed end of the cavity 46 isadjacent the bearing 50. The cavity 46 tapers outwardly as it extendstowards the end of the flywheel shaft 44. A feed tube 85 delivers theliquid coolant to the bottom end of the cavity 46. The shape of thecavity 46 causes the liquid coolant to flow along the side walls of thecavity 46 towards the end of the flywheel shaft 44 when the shaft 44rotates at a high speed. A collection manifold 90 connected to the inputside of the fluid reservoir 82 is disposed adjacent the open end of thecavity 46 to collect and recirculate the liquid coolant flowing from theopen end of the cavity 46 in the flywheel shaft 44. A labyrinth sealprovides a non-contact seal between the end of the flywheel shaft 44 andthe collection manifold 90.

The collection manifold 90 comprises a generally circular manifold withan opening 92 in the bottom wall thereof and one or more fluid outlets93 along the sidewall of the manifold 90 through which oil or liquidcoolant is recirculated. The feed tube 85 passes through an opening 96in the top wall of manifold 90, which is sealed by an o-ring seal 98.Additionally, a resilient deflector shield 95 is attached to the feedtube 85 to deflect fluid away from the opening 96 in the top wall of thecollection manifold 90. A rounded protrusion 94 is formed around theperimeter of the opening 92 on the interior side of the bottom wall ofthe manifold 90. As explained in more detail below, the roundedprotrusion 94 forms part of the labyrinth seal to prevent oil fromseeping into the interior of the enclosure 30.

In the embodiment shown in FIG. 9, a bell-shaped liner 120 is insertedinto each cavity 46 in the flywheel shaft 44. The liner 120 includes aflared end 122 that extends radially outward and over the roundedprotrusion 94 surrounding the opening 92 in the bottom of the collectionmanifold 90 with a gap between the flared end 122 and the roundedprotrusion 94 in the range of 1/128 inches to 1/32 inches to form thelabyrinth seal. The size of the gap and the rotation of the liner 120with the flywheel shaft 44 prevents fluid from migrating into theinterior of the enclosure 30. In the event that liquid coolant leakspast the labyrinth seal, it can be collected and returned by ascavenging circuit 88.

FIG. 10 illustrates an alternative system for forming a labyrinth seal.In this embodiment, a shoulder 48 is formed in the side wall of thefluid cavity 46 adjacent the open end of the flywheel shaft 44. Anannular sealing member 124, shown best in FIG. 10, is inserted into theopen end of the cavity 46. The inner surface of the sealing member 124bulges inwardly towards the axis of rotation of the flywheel shaft 44.As the liquid coolant flows towards the open end of the cavity 46, thefluid encounters the bulge, which directs the fluid flow towards theaxis of rotation of the flywheel shaft 44 and reduces the flow rate ofthe fluid. As a result, the liquid coolant remains in contact with theflywheel shaft 44 for a longer period of time and absorbs a greateramount of heat. The outer end of the sealing member 124 includes afinger-like element 126 that extends over the rounded protrusion 92surrounding the opening in the collection manifold 90 with a gap betweenthe finger-like element 126 and the rounded protrusion 94 in the rangeof 1/128 inches to 1/32 inches to form the labyrinth seal. As in theprevious embodiment, the size of the gap and the rotation of the sealingmember 124 prevent the liquid coolant from migrating into the interiorof the enclosure 30.

FIGS. 11 and 12 show embodiments similar to the embodiment in FIGS. 9and 10 with additional flow control features to control the flow ofliquid coolant from the cavities 46 in the ends of the shaft 44.Generally, the flow control features are design to slow down the flow ofoil or liquid coolant to provide sufficient time for heat exchange, i.e.for the transfer of heat from the shaft 44 to the oil or liquid coolant.In the embodiment shown in FIG. 11, a series of solid disks 130 areattached to the feed tube 85 and extend radially outward towards theliner 120. The flow of oil or liquid coolant is restricted to a smallgap between the outer edge or periphery of the disks 130 and the liner120. In the embodiment shown in FIG. 12, a porous material 132, such asa metal foam, is place in the cavity 46 in the flywheel shaft 44 with abore down the center for the feed tube 85. Oil or liquid coolantdelivered via the feed tube 85 flows back out through the porous metalfoam or other porous material 132, which transfers heat to the oil orliquid coolant. Other similar techniques may also be used to slow downthe flow of oil or liquid coolant to provide time for heat transfer.

In another embodiment, the bearing cooling system 100 comprises aconductive metal cap (not shown) is attached to the end of the flywheelshaft 44 that contacts the inner race 52 of the flywheel bearings 50. Inone embodiment, the metal cap further includes elongated conductiveelements that extend into similarly formed grooves in the flywheel shaft44 to conduct heat from the flywheel shaft 44 to the metal cap. Liquidcoolant is sprayed on to the metal cap. The rotation of the flywheelshaft 44 causes the liquid coolant to flow outward where it is collectedby a fluid collection system. A labyrinth seal provides a non-contactseal between the metal cap and the fluid collection system to reducefrictional forces acting on the flywheel shaft 44.

The bearing cooling systems 100 as herein described allow much greaterheat dissipation compared to current technology, which enables use of alarger motor 60 and lower operating temperature, even with the largermotor 60. The larger motor and lower operating temperature enable rapidspin up and spin down of the flywheel assembly 40, and a much lower timeto engage.

In use, the gimbal 20 is normally locked during spin up, i.e., while theflywheel assembly 40 is being accelerated, to prevent precession of theflywheel 42 until a predetermined rotational speed is achieved. Inconventional CMGs, the gimbal 20 is typically locked until the flywheelassembly 40 reaches 75-80% or more of the maximum rotational speed.Locking the gimbal 20 is necessary to prevent frictional losses whilethe flywheel assembly 40 is being accelerated. If the gimbal 20 in aconventional CMG is unlocked too early, the frictional losses willprevent the smaller motors from accelerating the flywheel assembly 40,or will greatly diminish the acceleration of the flywheel assembly 40resulting in a much longer spin up period.

The current state of the art in bearing cooling for a CMG 10 maintainedin a vacuum environment uses interwoven fins and relies primarily ongaseous conduction between the interwoven fins to dissipate the heat.See, e.g., U.S. Pat. Nos. 7,546,782 and 8,117,930. The reliance ongaseous conduction as the primary mode of heat transfer severely limitsthe amount of heat that can be dissipated since gaseous conduction isless efficient than liquid or solid conduction. The heat transfercapacity of the interwoven fins is also limited by the surface area ofthe interwoven fins. Less surface area means less heat transfercapacity. As the enclosure 30 of the CMG 10 shrinks is size, there isless space available for the interwoven fins. These factors place severelimits on the heat budget for the CMG 10.

There are two main sources of heat in the CMG 10: heat generated by themotor 60 inside the enclosure 30 and heat generated by bearing friction.A large percentage of the heat budget is needed to dissipate heat fromthe bearings 50 in order to prevent bearing failure. The remainingportion of the heat budget after accounting for bearing coolingdetermines the size of the motor 60 that can be used inside theenclosure 30. Thus, conventional CMGs 10 using interwoven fins for heatdissipation are limited in the size of the motor 60. If the motor 60 istoo large so that the heat transfer capacity of the interwoven fins isexceeded,

The limitation on the motor size results in a poor acceleration profilefor the flywheel 42 in CMGs 10, which in turn means a long waitingperiod before the CMG 10 can be used. A boater will typically desire touse the CMG 10 as soon as possible after getting underway. As notedpreviously, the CMG 10 is typically locked with the flywheel assembly 40in a vertical positions until the flywheel 42 reaches the minimumoperating speed (typically approximately 75% to 80% of its normaloperating speed) is reached. CMGs 10 currently on the market may take 30minutes or longer to reach the minimum operating speed at which theflywheel 42 can be engaged, while many boat trips, particularity onsmaller boats are 30 minutes or less. This means the waiting periodbefore the time to engage (unlock the flywheel assembly 40) is reachedis longer than many boat trips.

The size of the motor 60 in conventional CMGs 10 place a floor on theminimum operating speed at which the CMG 10 can be engaged (i.e.,unlocked). The CMG 10 is typically locked to prevent precession when theflywheel assembly 40 is being accelerated. The CMG 100 can be locked toprevent rotation of the enclosure 30 by the active braking system 78.When the CMG 10 is unlocked, the precession of the flywheel 42 willplace large side loads on the bearings 50. The bearing friction from theside loading of the bearings 50 that must be overcome by the motor 60,which will dramatically decrease the already slow acceleration rate. Thelower acceleration rate means that the time to reach the normaloperating speed could be in the order or several hours instead of ten ofminutes, which would not be acceptable to a typically boater. In somecases, the frictional load may be too for the motor 60 to overcome sothat the further acceleration of the flywheel assembly 40 becomesimpossible and the normal operating speed cannot be reached.

Another consideration is that the power to the motor 60 is at itsmaximum when the flywheel assembly 40 is being accelerated, and isreduced when the flywheel assembly 40 reaches its normal operatingspeed. Thus, more heat is generated by the motor 60 when it isaccelerating. The additional heat generated by the motor 60 also limitsthe time to engage because the additional heat from the motor 60 mayexceed the design limits of the bearing cooling system.

The bearing cooling systems 100 as described herein enable moreefficient heat transfer, which enables a far greater heat transfercapacity and a greatly increased heat budget. The increased heat budgetmeans that larger and more powerful motors 60 that generate more heatcan be used without fear of a bearing failure. With a larger and morepowerful motor 60, the CMG 10 is able to achieve greater acceleration ofthe flywheel assembly 40 and much lower time to engage than aconventional CMG 10. In addition to the higher rates of acceleration,which naturally lead to lower times to engage assuming the same minimumoperating speed, a larger motor 60 enables the flywheel assembly 40 at alower operating speed, which further reduces the time to engage, becausethe larger motor 60 is able to overcome the additional friction from theloading of the bearings 50. For example, a motor 60 rated at 10,000 to15,000 watts could potentially achieve a time to engage rates in theorder of a few minutes.

As one example, the flywheel assembly 40 described above with a momentof inertia equal to about 32,273 lb in² can be accelerated from rest to9000 rpm in about 30 minutes or less, which equates to an averageacceleration of about 5 rpm/s or more, and preferably in about 20minutes or less, which equates to an average acceleration of about 7.5rpm/s or more, and even more preferably in about 10 minutes or less,which equates to an average acceleration of about 15 rpm/s or more.Additionally, the time to engage for the CMG 10 as herein described ismuch shorter because the motor 60 is powerful enough to overcome thefrictional losses when the gimbal 20 is unlocked. For example, in aflywheel assembly 40 with a moment of inertia equal to about 32,273 lbin², the time to engage (assuming 75% of operating speed) is less thanabout 20 minutes, and more preferably less than about 10 minutes, andeven more preferably less than 5 minutes. The rapid spin up and shortertime to engage enables beneficial use of the CMG 10 even for short triptimes, which makes up a majority of boating trips. Thus, the rapidspin-up enables the CMG 10 to be used on a far greater number of boatingoccasions.

Similarly, the spin down is in the order of minutes rather than hourscompared to the current technology. Cooling systems with interleavedfins that rely on gaseous conduction and convection operate at a hightemperature (e.g. 400 degrees F.) and dissipate heat relatively slowly.In such systems, if the flywheel is stopped too fast, the heat may causecomponents too warp, which in turn may cause bearing life to beshortened to months or days as opposed to years. The cooling system asherein describe enables the CMG 10 to operate at a lower temperature(e.g. 200 degrees F.) and is extremely efficient at removing heat.Consequently, the spin down time is cut from 3-5 hours to just a fewminutes. This reduced running temperature as well as the rapid cooldownperiod prevents the extremely well balanced rotating components fromwarping and thus the spin down time is greatly reduced. The short spindown time eliminates the annoying hum and vibration from the spinningflywheel and allows enjoyment of the peace and serenity after returningfrom a day of boating.

Generally, CMGs 10 with relatively small flywheels operate at higherrotational speeds than CMGs 10 with larger flywheels. The smaller CMGs10 typically include flywheels weighing 700 lbs or less rotating at 9000rpm or more and with a moment of inertia less than 40,000 lb in². Thesmaller CMGs 10 typically include flywheels 42 weighing 700 lbs or lessrotating at 9000 rpm or more and with a moment of inertia less than40,000 lb in². The larger CMGs 10 typically include flywheels 42weighing greater than 700 lbs rotating at less than 9000 rpm with amoment of inertia greater than 40,000 lb in².

Table 1 below shows the spin-up time and time to engage for eightdifferent CMGs 100 where the acceleration rate is 5 rpm/s for thesmaller CMGs 10 and 2.5 rpm/s for the larger CMGs 10. The time to engageis assumed to be at the point when the flywheel assembly 40 reaches 75%of its normal operating speed.

TABLE 1 Spin-up Time and Time to Engage-Example 1 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 22.5 30 125  <40 9000 5 Model 2 22.530 250 40-60 9000 5 Model 3 22.5 30 325 60-90 9000 5 Model 4 22.5 30 425 90-200 9000 5 Model 5 22.5 30 600 200-500 9000 5 Model 6 30 40 1000500-800 6000 2.5 Model 7 30 40 1500  800-1200 6000 2.5 Model 8 30 401900 >1200 6000 2.5

Table 2 below shows the spin-up time and time to engage for eightdifferent CMGs 100 where the acceleration rate is 10 rpm/s for thesmaller CMGs 10 and 5 rpm/s for the larger CMGs 10. The time to engageis assumed to be at the point when the flywheel assembly 40 reaches 75%of its normal operating speed.

TABLE 2 Spin-up Time and Time to Engage Example 2 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 11.25 15 125  <40 9000 10 Model 211.25 15 250 40-60 9000 10 Model 3 11.25 15 325 60-90 9000 10 Model 411.25 15 425  90-200 9000 10 Model 5 11.25 15 600 200-500 9000 10 Model6 15 20 1000 500-800 6000 5 Model 7 15 20 1500  800-1200 6000 5 Model 815 20 1900 >1200 6000 5Table 3 below shows the spin-up time and time to engage for eightdifferent CMGs 100 where the acceleration rate is 5 rpm/s for thesmaller CMGs 10 and 7.5 rpm/s for the larger CMGs 10. The time to engageis assumed to be at the point when the flywheel assembly 40 reaches 75%of its normal operating speed.

TABLE 3 Spin-up Time and Time to Engage Example 3 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 7.5 10 125  <40 9000 15 Model 2 7.510 250 40-60 9000 15 Model 3 7.5 10 325 60-90 9000 15 Model 4 7.5 10 425 90-200 9000 15 Model 5 7.5 10 600 200-500 9000 15 Model 6 10 13.33 1000500-800 6000 7.5 Model 7 10 13.33 1500  800-1200 6000 7.5 Model 8 1013.33 1900 >1200 6000 7.5

Table 4 below shows the spin-up time and time to engage for eightdifferent CMGs 100 where the acceleration rate is 2.5 rpm/s for thesmaller CMGs 10 and 5 rpm/s for the larger CMGs 10. The time to engageis assumed to be at the point when the flywheel assembly 40 reaches 75%of its normal operating speed.

TABLE 4 Spin-up Time and Time to Engage Example 4 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 5.625 7.5 125  <40 9000 20 Model 25.625 7.5 250 40-60 9000 20 Model 3 5.625 7.5 325 60-90 9000 20 Model 45.625 7.5 425  90-200 9000 20 Model 5 5.625 7.5 600 200-500 9000 20Model 6 7.5 10 1000 500-800 6000 10 Model 7 7.5 10 1500  800-1200 600010 Model 8 7.5 10 1900 >1200 6000 10

In the examples shown in Tables 1-4, it is assumed that the CMG 10 isengaged, i.e. unlocked, when the flywheel assembly 40 reaches 75% of itsnormal operating speed. One of the advantages of the present disclosureis that larger motors 60 can be used that are able overcome frictionallosses in the bearings 50 when the CMG 10 is unlocked. Thus, the time toengage can be reduced even more by unlocking the CMG 10 when theflywheel assembly reaches 50% of its normal operating speed, or even 25%of its normal operating speed.

Tables 5-8 show the time to engage in scenarios where the CMG 10 isunlocked at 50% of normal operating speed.

TABLE 5 Spin-up Time and Time to Engage-Example 5 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 15 30 125  <40 9000 5 Model 2 15 30250 40-60 9000 5 Model 3 15 30 325 60-90 9000 5 Model 4 15 30 425 90-200 9000 5 Model 5 15 30 600 200-500 9000 5 Model 6 20 40 1000500-800 6000 2.5 Model 7 20 40 1500  800-1200 6000 2.5 Model 8 20 401900 >1200 6000 2.5

TABLE 6 Spin-up Time and Time to Engage Example 6 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 7.25 15 125  <40 9000 10 Model 27.25 15 250 40-60 9000 10 Model 3 7.25 15 325 60-90 9000 10 Model 4 7.2515 425  90-200 9000 10 Model 5 7.25 15 600 200-500 9000 10 Model 6 10 201000 500-800 6000 5 Model 7 10 20 1500  800-1200 6000 5 Model 8 10 201900 >1200 6000 5

TABLE 7 Spin-up Time and Time to Engage Example 7 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 5 10 125  <40 9000 15 Model 2 5 10250 40-60 9000 15 Model 3 5 10 325 60-90 9000 15 Model 4 5 10 425 90-200 9000 15 Model 5 5 10 600 200-500 9000 15 Model 6 6.67 13.33 1000500-800 6000 7.5 Model 7 6.67 13.33 1500  800-1200 6000 7.5 Model 8 6.6713.33 1900 >1200 6000 7.5

TABLE 8 Spin-up Time and Time to Engage Example 8 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 3.75 7.5 125  <40 9000 20 Model 23.75 7.5 250 40-60 9000 20 Model 3 3.75 7.5 325 60-90 9000 20 Model 43.75 7.5 425  90-200 9000 20 Model 5 3.75 7.5 600 200-500 9000 20 Model6 5 10 1000 500-800 6000 10 Model 7 5 10 1500  800-1200 6000 10 Model 85 10 1900 >1200 6000 10

Tables 9-12 show the time to engage in scenarios where the CMG 10 isunlocked at 50% of normal operating speed.

TABLE 9 Spin-up Time and Time to Engage-Example 9 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 7.5 30 125  <40 9000 5 Model 2 7.530 250 40-60 9000 5 Model 3 7.5 30 325 60-90 9000 5 Model 4 7.5 30 425 90-200 9000 5 Model 5 7.5 30 600 200-500 9000 5 Model 6 10 40 1000500-800 6000 2.5 Model 7 10 40 1500  800-1200 6000 2.5 Model 8 10 401900 >1200 6000 2.5

TABLE 10 Spin-up Time and Time to Engage Example 10 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 3.75 15 125  <40 9000 10 Model 23.75 15 250 40-60 9000 10 Model 3 3.75 15 325 60-90 9000 10 Model 4 3.7515 425  90-200 9000 10 Model 5 3.75 15 600 200-500 9000 10 Model 6 5 201000 500-800 6000 5 Model 7 5 20 1500  800-1200 6000 5 Model 8 5 201900 >1200 6000 5

TABLE 11 Spin-up Time and Time to Engage Example 11 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 2.5 10 125  <40 9000 15 Model 2 2.510 250 40-60 9000 15 Model 3 2.5 10 325 60-90 9000 15 Model 4 2.5 10 425 90-200 9000 15 Model 5 2.5 10 600 200-500 9000 15 Model 6 3.33 13.331000 500-800 6000 7.5 Model 7 3.33 13.33 1500  800-1200 6000 7.5 Model 83.33 13.33 1900 >1200 6000 7.5

TABLE 12 Spin-up Time and Time to Engage Example 12 Time to MomentAcceler- engage Spin-up Weight of Inertia Speed ation (min) time (min)(lbs) (lb ft²) RPM) (RPM/s) Model 1 >2 7.5 125  <40 9000 20 Model 2 >27.5 250 40-60 9000 20 Model 3 >2 7.5 325 60-90 9000 20 Model 4 >2 7.5425  90-200 9000 20 Model 5 >2 7.5 600 200-500 9000 20 Model 6 2.5 101000 500-800 6000 10 Model 7 2.5 10 1500  800-1200 6000 10 Model 8 2.510 1900 >1200 6000 10

The bearing cooling systems 100 as herein described enable fasteracceleration rates for the flywheel assembly 40, which translates to alower time to engage the CMG 10. The lower time to engage in turn willenable beneficial use of the CMG 10 even on trips of short duration. Forsmaller units, the bearing cooling system 100 is effective to enable aflywheel assembly 40 with a moment of inertia less than 40,000 lb in² tobe accelerated at a rate of 5 rpm/s or greater. Accelerations ratesgreater than 30 rpm/s for the smaller units are achievable. For largerunits, the bearing cooling system is effective to enable a flywheelassembly 40 with a moment of inertia greater than 40,000 lb in² to beaccelerated at a rate of 2.5 rpm/s or greater. Accelerations ratesgreater than 15 rpm/s for the larger units are achievable. The bearingcooling system also enable fast spin down times so that the quietenjoyment of the boat is not disturbed by the noise emanating from theflywheel assembly 40 as it winds down.

1. A gyroscopic roll stabilizer for a boat, said gyroscopic stabilizercomprising: an enclosure mounted to a gimbal for rotation about a gimbalaxis and configured to maintain a below-ambient pressure; a flywheelassembly including a flywheel and flywheel shaft; one or more bearingsfor rotatably mounting the flywheel assembly inside the enclosure; amotor for rotating the flywheel assembly; an open-ended cavity formed inan end of the flywheel shaft; and a heat transfer member extending intothe cavity for transferring heat from the flywheel shaft to an exteriorof the enclosure.
 2. The gyroscopic roll stabilizer of claim 1 whereinthe heat transfer member is a rotating member in surface contact withwalls of the cavity such that heat is transferred from the flywheelshaft to the heat transfer member by solid conduction.
 3. The gyroscopicroll stabilizer of claim 2 further comprising a stationary heat transfermember having a first end adjacent an end of the rotating heat transfermember to enable heat transfer from the rotating heat transfer member tothe stationary heat transfer member and a second end connected to a heatexchange plate outside of the enclosure.
 4. The gyroscopic rollstabilizer of claim 2 further comprising a grease film between therotating and stationary components of the heat transfer member.
 5. Thegyroscopic roll stabilizer of claim 1 wherein the heat transfer memberis spaced from the walls of the cavity.
 6. The gyroscopic rollstabilizer of claim 5 further comprising a liquid heat transfer mediumcontained in a gap between the heat transfer member and the walls of thecavity such that heat is transferred from the flywheel shaft to the heattransfer member by conduction through the liquid heat transfer medium.7. The gyroscopic roll stabilizer of claim 6 wherein the heat transfermedium comprises a low vapor oil.
 8. The gyroscopic roll stabilizer ofclaim 6 wherein the heat transfer member connects to a heat exchangeplate outside of the enclosure and transfers heat by solid to the heatexchange plate.
 9. The gyroscopic roll stabilizer of claim 1 wherein themotor is configured to provide a time to engage the gyroscopic rollstabilizer when the flywheel assembly is accelerated from rest of 20minutes or less.
 10. The gyroscopic roll stabilizer of claim 1 whereinthe motor is configured to provide a time to engage the gyroscopic rollstabilizer when the flywheel assembly is accelerated from rest of 10minutes or less.
 11. The gyroscopic roll stabilizer of claim 1 whereinthe motor is configured to provide a time to engage the gyroscopic rollstabilizer when the flywheel assembly is accelerated from rest of 5minutes or less.
 12. The gyroscopic roll stabilizer of claim 1 whereinthe motor is configured to provide a time to engage the gyroscopic rollstabilizer when the flywheel assembly reaches 50% or less of its normaloperating speed.
 13. The gyroscopic roll stabilizer of claim 1 whereinthe motor is configured to provide a time to engage the gyroscopic rollstabilizer when the flywheel assembly reaches 25% or less of its normaloperating speed.
 14. A gyroscopic roll stabilizer for a boat, saidgyroscopic stabilizer comprising: an enclosure mounted to a gimbal forrotation about a gimbal axis and configured to maintain a below-ambientpressure; a flywheel assembly including a flywheel and flywheel shaft;one or more bearings for rotatably mounting the flywheel assembly insidethe enclosure; a motor for rotating the flywheel assembly; an open-endedcavity formed in an end of the flywheel shaft; a coolant delivery systemfor delivering a liquid coolant to the cavity; and a collection systemdisposed adjacent the end of the flywheel shaft for collecting theliquid coolant delivered to the cavity of the flywheel shaft.
 15. Thegyroscopic roll stabilizer of claim 14 wherein the cavity tapersoutwardly from a bottom of the cavity to the end of the flywheel shaftso liquid coolant delivered to the cavity via the feed tube flows bycentrifugal force toward the liquid coolant collection system.
 16. Thegyroscopic roll stabilizer of claim 14 further comprising one or morediscs attached to the feed tube and configured to restrict the liquidcoolant flow in the cavity.
 17. The gyroscopic roll stabilizer of claim16 wherein the liquid coolant flow is restricted to a space between theouter surface of the discs and the inner surface of the cavity.
 18. Thegyroscopic roll stabilizer of claim 14 further comprising a porous metalfoam disposed in the cavity to restrict the liquid coolant flow in thecavity.
 19. The gyroscopic roll stabilizer of claim 14 wherein the motoris configured to provide a time to engage the gyroscopic roll stabilizerwhen the flywheel assembly is accelerated from rest of 20 minutes orless.
 20. The gyroscopic roll stabilizer of claim 14 wherein the motoris configured to provide a time to engage the gyroscopic roll stabilizerwhen the flywheel assembly is accelerated from rest of 10 minutes orless.
 21. The gyroscopic roll stabilizer of claim 14 wherein the motoris configured to provide a time to engage the gyroscopic roll stabilizerwhen the flywheel assembly is accelerated from rest of 5 minutes orless.
 22. The gyroscopic roll stabilizer of claim 14 wherein the motoris configured to provide a time to engage the gyroscopic roll stabilizerwhen the flywheel assembly reaches 50% or less of its normal operatingspeed.
 23. The gyroscopic roll stabilizer of claim 14 wherein the motoris configured to provide a time to engage the gyroscopic roll stabilizerwhen the flywheel assembly reaches 25% or less of its normal operatingspeed.
 24. A method of cooling bearings in a gyroscopic boat rollstabilizer, said method comprising: rotating a flywheel assembly in anenclosure mounted in a gimbal for rotation about a gimbal axis andmaintained at below ambient pressure to provide a counter torque forroll stabilization, said flywheel assembly including a flywheel and aflywheel shaft; transferring heat generated by bearings supporting theflywheel assembly through the flywheel shaft to a heat transfer memberextending into a cavity in one end of the flywheel shaft; andtransferring the heat by solid conduction through the heat transfermember to an exterior of the enclosure.
 25. The method of claim 24wherein the heat transfer member rotates with the flywheel assembly andis in surface contact with walls of the cavity such that heat istransferred from the flywheel shaft to the heat transfer member by solidconduction.
 26. The method of claim 25 wherein transferring the heat bysolid conduction through the heat transfer member to an exterior of theenclosure comprises: transferring the heat to a stationary heat transfermember; and transferring the heat from the stationary heat transfermember to a heat exchange plate disposed outside the enclosure.
 27. Themethod of claim 26 wherein transferring the heat to a stationary heattransfer member comprises transferring the heat through a grease filmbetween the rotating heat transfer member and the stationary heattransfer member.
 28. The method of claim 24 wherein transferring heatgenerated by bearings supporting the flywheel assembly through theflywheel shaft to a heat transfer member comprises transferring the heatacross a gap between the flywheel shaft and the heat transfer member.29. The method of claim 28 wherein the gap is contains a heat transfermedium and the heat is transferred from the flywheel shaft to the heattransfer member by liquid conduction.
 30. The method of claim 29 whereinthe heat transfer medium is a low vapor oil.
 31. The method of claim 29wherein the heat transfer member connects to a heat exchange plate andtransfers heat by solid conduction to the heat exchange plate.
 32. Themethod of claim 24 further comprising: accelerating the flywheelassembly from rest; and engaging the gyroscopic roll stabilizer in lessthan 20 minutes from the start of acceleration.
 33. The method of claim24 further comprising: accelerating the flywheel assembly from rest; andengaging the gyroscopic roll stabilizer in less than 10 minutes from thestart of acceleration.
 34. The method of claim 24 further comprising:accelerating the flywheel assembly from rest; and engaging thegyroscopic roll stabilizer in less than 5 minutes from the start ofacceleration.
 35. The method of claim 24 further comprising:accelerating the flywheel assembly from rest; and engaging thegyroscopic roll stabilizer when the flywheels assembly reaches 505 orless of normal operating speed.
 36. The method of claim 24 furthercomprising: accelerating the flywheel assembly from rest; and engagingthe gyroscopic roll stabilizer when the flywheels assembly reaches 505or less of normal operating speed.
 37. A method of cooling bearings in agyroscopic boat roll stabilizer, said method comprising: rotating aflywheel assembly in an enclosure mounted in a gimbal for rotation abouta gimbal axis and maintained at below ambient pressure to provide acounter torque for roll stabilization, said flywheel assembly includinga flywheel and a flywheel shaft; circulating a liquid coolant through acavity formed in one end of the flywheel shaft; and transferring heatgenerated by bearings supporting the flywheel assembly through theflywheel shaft to the liquid coolant.
 38. The method of claim 37 whereincirculating the liquid coolant through the cavity formed in one end ofthe flywheel shaft comprises: delivering the liquid coolant to thecavity through an open end of the cavity; flowing the liquid coolantalong a wall of the cavity from a bottom end of the cavity towards theopen end so such that heat is transferred from the flywheel shaft to theliquid coolant.
 39. The method of claim 38 further comprising collectingand recirculating the liquid coolant flowing from the open end of thecavity.
 40. The method of claim 38 wherein the wall of the cavity tapersoutwardly from the bottom end to the open end and wherein flowing theliquid coolant along a wall of the cavity comprises applying centrifugalforce to the liquid coolant to flow the liquid coolant along the wallsof the cavity from the bottom end towards the open end.
 41. The methodof claim 38 wherein delivering a liquid coolant to the cavity comprisesdelivering the liquid coolant to a bottom end of the cavity through afeed tube extending along a longitudinal axis of the flywheel shaft. 42.The method of claim 41 further comprising slowing the flow of the liquidcoolant in the cavity.
 43. The method of claim 42 wherein slowing theflow of the liquid coolant in the cavity comprises restricting the flowof liquid coolant to a gap between the outer edge of one or more disksattached to the feed tube and the wall of the cavity.
 44. The method ofclaim 42 wherein slowing the flow of the liquid coolant in the cavitycomprises flowing the liquid coolant through a porous material placedinside the cavity.
 45. The method of claim 38 wherein the porousmaterial comprises a porous metal foam.
 46. The method of claim 37further comprising: accelerating the flywheel assembly from rest; andengaging the gyroscopic roll stabilizer in less than 20 minutes from thestart of acceleration.
 47. The method of claim 37 further comprising:accelerating the flywheel assembly from rest; and engaging thegyroscopic roll stabilizer in less than 10 minutes from the start ofacceleration.
 48. The method of claim 37 further comprising:accelerating the flywheel assembly from rest; and engaging thegyroscopic roll stabilizer in less than 5 minutes from the start ofacceleration.
 49. The method of claim 37 further comprising:accelerating the flywheel assembly from rest; and engaging thegyroscopic roll stabilizer when the flywheels assembly reaches 505 orless of normal operating speed.
 50. The method of claim 37 furthercomprising: accelerating the flywheel assembly from rest; and engagingthe gyroscopic roll stabilizer when the flywheels assembly reaches 505or less of normal operating speed.